A variety of different types of network configurations have been proposed or used for transmitting data between interconnected nodes in a network. For example, Local Area Networks (LANs) comprise a number of computer based pieces of equipment which are normally distributed within a single establishment. ALAN is most commonly arranged into one of three basic topologies, namely star, bus and ring. More complex network configurations are possible by interconnecting a number of different LANs by means of switches in the form of bridges or routers.
There are a number of different protocols which define the method by which data and commands in the form of messages are transferred from one node to another in a network. In most network protocols, the usual method of routing messages between nodes is to include header information as part of the message which header specifies the address of the destination node and often the address of the node from which the message originates (source address). The addresses specified in the header are those unique addresses which have been assigned to the nodes when the network is configured. In some network schemes, it is necessary to assign a value to a particular node by means of a switch. In a network comprising a number of ring networks interconnected via some form of switch, the address information will commonly have two components identifying the target network and the destination node within the target network.
When a message is sent through a network from a source node to a destination, each node receiving the message processes the destination address information to determine whether the address matches the unique address assigned to that node at power-on. If there is no match, the node forwards the message onto the next (downstream) node which then processes the address information in the same way, In a ring configuration, all the component nodes are generally dual-ported and there is thus no requirement on the nodes to determine on which output path the message should be forwarded. However, in other topologies, in which the component nodes may be single-ported, dual-ported or switch nodes comprising three or more ports, the switch node will contain routing hardware which must determine the identity of the output port for any particular message. In some routing schemes, the switch compares the destination address in the message with a list of addresses contained in a table in order to determine the output node.
There are a number of disadvantages inherent in previously used routing methods. For example, the routing hardware required at each node to store its unique address, to extract the destination address from the incoming message, and to compare the extracted address with the unique node address is necessarily complex. In a switch node, the hardware is even more complex to enable parsing of the incoming message for the unique identity of the output port from which the message is to be further transmitted. Previously used methods also require the assignment of the unique node addresses at power on, which is sometimes accomplished by the inconvenient means of manual switches.